In the field known as “hydroforming”, it is known to use a pressurized liquid injected inside a preform placed in a mold to shape a container according to the shape of the mold and fill said shaped container with the liquid at the same time. Advantageously, the injected liquid is the end product contained in the container, i.e. the product which is intended to be provided to a consumer using the container.
For allowing the deformation of the preform into a container, the preform is heated at a temperature greater than the glass transition temperature and lower than the crystallization temperature of the material of the preform such that the preform is placed in a malleable state and is able to expand up to the shape of the container to be produced.
In some application, the liquid injected in the preform is generally injected at a temperature lower than the glass transition temperature of the preform material. The temperature of the injected liquid is for example the ambient temperature, typically from 5° C. up to 50° C. while the glass transition temperature is for example over 75° C. for PET.
The preform is expanded in an axial direction, i.e. along the axis of the preform, and in radial planes, i.e. perpendicularly to the axial direction, according to a bi-orientation ratio, or stretch ratio, which is defined by the following equation:
  BOR  =            D      d        ×          L      l      
Wherein BOR is the bi-orientation ratio, D is the mean diameter of the container to be produced, d is the mean diameter of the preform, L is the half developed length of the container to be produced and l is the half developed length of the preform.
In order to obtain a container having good mechanical and gas/liquid barrier properties and presenting a satisfactory shape, the bi-orientation ratio has to be optimized.
In a hydroforming process, the axial expansion of the preform can be assisted by a stretch rod arranged to elongate the preform along its axis, but the radial expansion is promoted only by the injected liquid and can be insufficient in some areas in the preform. The liquid is generally injected in the direction of the preform axis, generally a vertical axis, and reaches the bottom of the preform first. Consequently, the bottom part of the preform is first expanded and the expansion of the preform occurs from bottom to top the container. Since during the liquid injection, the expanding preform cools down, the upper part of the container can be insufficiently expanded at the end of the liquid injection.
In this case, the bi-orientation ratio is not optimized and the shape of the produced container is not satisfactory.
One of the aims of the invention is to improve the radial expansion of the preform in order to optimize the bi-orientation ratio and ensure a better forming of the container.
Far from the above problem of forming performance, document US 2013/0074979 describes an apparatus for filling bottles. The apparatus comprises a liquid valve, a swirl body and a probe determining the fill level of liquid inside the bottle during filling. The swirl body imparts a swirl such that the liquid filling material flows along the inner surface of the container, avoiding a premature wetting of the probe by the liquid filling material before the desired fill level is reached.